Pros
Ability to work on projects that do not exist anywhere else: Hubble Space Telescope, International Space Station, and so on. Research is cutting edge, redefining the boundaries of science and rewriting textbooks with discoveries we make in Earth Science, Global Climate Change, Nanotechnology, Electronics Research, Planetary Science, and much more. As a new hire you could have the opportunity to do very significant contributions and there are tracks to jump into a very important position at a very early age if you prove yourself competent and responsible.
Cons
There are some really innovative ambitious people, but there still is a lot of dead-weight of those who just come into work and do the bare minimum, but do not really contribute to NASA as a organization moving forward.